HLCS (EC 6.3.4.10) catalyzes the biotinylation
of biotin-dependent mitochondrial carboxylases. In
mammals, there are four carboxylases that require
biotinylation: acetyl-CoA carboxylase, pyruvate
carboxylase, propionyl-CoA carboxylase and
3-methylcrotonyl-CoA carboxylase. These carboxylases
are essential for cellular biosynthesis.
Therefore, defects in HLCS, which reduce the
biotin-dependent enzyme activity, affect several
important metabolic processes. HLCS is encoded
by an 11-exon gene, HLCS, located on chromosome
21q22.1. To date, there are at least 35 mutations
reported in HLCS (http://www.hgmd.cf.ac.uk,
accessed August 2009).
Here, we report four Thai patients with MCD.
All of them were diagnosed to have HLCS
deficiency. Treatment with low dose of biotin
was able to significantly improve their clinical